Copper alloy, method of producing the same, and copper tube

ABSTRACT

Copper alloys, methods for producing copper alloys, and copper tubes are provided. The copper alloys include an alpha solid solution formed from phosphorous deoxidized copper and at least one trace element comprising tin. The content of tin ranges from about 0.1% to about 2.0% by weight of the copper alloy. The trace element can further include zinc in an amount from about 0.05% to about 1.0% by weight of the copper alloy. The copper alloys have an increased tensile strength due to the strengthening effect by the alpha solid solution formed by phosphorous deoxidized copper and tin as the trace element, and accordingly a copper tube made from the copper alloy has a significantly improved pressure resistance.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §119 to Chinese Patent Application No. 200910135785.2, titled “Copper alloy, method of producing the same, and copper tube,” filed Apr. 29, 2009. The complete disclosure of the foregoing priority application is hereby fully incorporated herein by reference.

TECHNICAL FIELD

The present invention relates generally to a nonferrous metal materials. More particularly, the present invention is directed to copper alloys, methods of producing the copper alloys, and copper tubes.

BACKGROUND

Copper tubes for air-conditioner cooling, or air-conditioner tubes, are tubing materials that are specially used in heat exchangers of cooling systems such as air-conditioners. Such tubing materials generally include plain tubings and tubings having various interior/exterior surface shapes, such as inner grooved tubes and fin tubes.

Conventional copper tubes for air-conditioner cooling are produced from phosphorous deoxidized copper. Phosphorous deoxidized copper has a tensile strength that ranges from about 205 to about 255 megapascal (MPa), in soft state, at ambient temperature. The phosphorous deoxidized copper has two specifications, including U.S. C12000 (or China TP1) and U.S. C12200 (or China TP2). The copper specification C12000 contains greater than or equal to 99.9 percent (%) of copper (Cu) and 0.004% to about 0.012% of phosphorus (P); while the copper specification C12200 contains greater than or equal to 99.9% of copper and 0.015% to about 0.040% of phosphorus. In both of these specifications of phosphorous deoxidized copper, the content of the element tin (Sn) is less than 0.005%, and the content of zinc (Zn) is less than 0.001%.

The two specifications of phosphorous deoxidized copper generally have appropriate toughness, welding behavior, strength, compactness, and corrosion resistance for use in air-conditioner cooling. However, there are a number of concerns with the use phosphorous deoxidized copper. For example, conventional tubings for air-conditioner cooling are lower in weight and have thin walls so to save on material expenses. However, a thinner wall leads to less pressure resistance, and thus these tubings have reduced service life and reduced reliability. With the development and application of environmentally friendly high-pressure refrigerants, heat-transfer tubings generally require higher pressure resistance. For example, a common refrigerant in home air-conditioners is HCFC-22 (also known as R-22), which has been used as a refrigerant for decades and is known to destroy the ozonosphere. In comparison, novel, environmentally friendly refrigerants, such as R407c and R410a, do not destroy the ozonosphere and have improved refrigerating and heating efficiencies, which are recognized in the international refrigeration industry as the optimal refrigerants for home air-conditioners. Furthermore, these novel refrigerants facilitate the miniaturization of air-conditioning systems, and thus reduce the material expenses incurred by manufacturers. However, the high pressure and the low pressure for the environmentally friendly refrigerants R407c and R410a are 3.0 MPa and 1.2 MPa respectively, which are about 1.5 times those pressures for the traditional refrigerant R22. Another consideration when designing air-conditioner tubes is related to the increasing attention to environmental pollution being paid to refrigerants, as humans increasingly focus on air pollution. Therefore, as more users appeal to nonhazardous refrigerants, the use of common refrigerants for air-conditioners is greatly limited. Refrigerants having desired thermodynamics without producing air pollution are urgently needed. Among varieties of refrigeration media in consideration, liquid carbon dioxide (CO₂) becomes the first alternative refrigerant in vehicle air-conditioners due to its unique ability to absorb a considerable amount of heat during vaporization without polluting the atmosphere upon release of carbon dioxide gas. However, one of the limitations for using CO₂ as the refrigerant in air-conditioners is that the air-conditioning systems have to work at relatively high pressures, at about five times the pressure in traditional systems, and thus, challenge the pressure resistance of air-conditioner tubes.

Therefore, a need exists for air-conditioner tubes having improved pressure resistance, and that meet the requirements for the use in air-conditioners.

SUMMARY OF THE INVENTION

The air-conditioner tubes described herein have improved pressure resistance over conventional tubings made from phosphorous deoxidized copper.

In one aspect, a copper alloy can include alpha solid solution formed by phosphorous deoxidized copper and at least one trace element comprising tin. Preferably, the content of tin is from about 0.1% to about 2.0% by weight of the copper alloy. Preferably, the trace elements further comprise zinc, the content of which is from about 0.05% to about 1.0% by weight of the copper alloy. The copper alloys of the present invention have an increased tensile strength over conventional copper alloys, due to the strengthening effect by the alpha solid solution formed by phosphorous deoxidized copper and the trace element tin

In another aspect, the present invention discloses a method for producing a copper alloy of the present invention. The method includes the steps of pre-heating at least one trace element comprising tin to remove the moisture in the trace element, adding the trace element into a molten solution of phosphorous deoxidized copper, and homogenizing, casting, and cooling the solution comprising the trace element, to produce a copper alloy comprising alpha solid solution. Preferably, the step of adding the trace element into the molten solution of phosphorous deoxidized copper comprises adding tin, the amount of which is from about 0.1% to about 2.0% by weight of the alloy to be produced, into the molten solution of phosphorous deoxidized copper. Preferably, the trace elements further comprise zinc, and the step of adding the trace elements into the molten solution of phosphorous deoxidized copper further comprises adding zinc, the amount of which is from about 0.05% to about 1.0% by weight of the alloy to be produced, into the molten solution of phosphorous deoxidized copper.

In yet another aspect, tubes are constructed from a copper alloy comprising alpha solid solution formed by phosphorous deoxidized copper and at least one trace element comprising tin. Preferably, the content of tin is from about 0.1% to about 2.0% by weight of the copper alloy. Preferably, the trace elements further comprise zinc, the content of which is from about 0.05% to about 1.0% by weight of the copper alloy. The copper tubes of the present invention have a significantly improved pressure resistance over conventional tubes for air-conditioners.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a method for producing a copper alloy, according to an exemplary embodiment.

FIG. 2 depicts a method for producing a copper alloy, according to another exemplary embodiment.

DETAILED DESCRIPTION OF THE INVENTION

A copper alloy described herein generally includes a trace element added to a phosphorous deoxidized copper matrix in a ratio such that the resulting alpha solid solution in the matrix has an increased tensile strength due to strengthening effect by the solid solution. Copper tubes for air-conditioners constructed from a copper alloy of the present invention have a significantly improved pressure resistance over conventional tubes for air-conditioners.

In certain embodiments, the element tin (Sn) may be added to phosphorous deoxidized copper to effectively improve the mechanical properties of the copper alloy by means of solid solution strengthening. In certain exemplary embodiments, the content of Sn is from about 0.1% to about 2.0% by weight of the alloy. Conventional alloys typically include a content of Sn that is less than about 0.1% by weight of the alloy, and the solid solution strengthening effect exhibits no significant advantage. Furthermore, in the instance that the content of Sn is greater than 2.0% by weight of the alloy, the tensile strength of the resulting alloy material is improved, however, the properties of the alloy material severely impede the machining of the material, and accordingly, would hinder tubing production.

In certain embodiments, the element zinc (Zn) may be added to phosphorous deoxidized copper, which further improves the solid solution strengthening, and has improved mechanical properties. Moreover, the addition of Zn may reduce the size of crystal grains, which may improve mechanical properties of the alloy material. In certain exemplary embodiments, the content of Zn added may be about 1.0% by weight of the alloy, where the content of Sn is 0.1% by weight of the alloy. In an alternative embodiment, the content of Zn added may be 0.05% by weight of the alloy, where the content of Sn is 2.0% by weight of the alloy. That is, the content of Zn added may range from about 0.05% to about 1.0% by weight of the alloy, where the content of Sn ranges from about 0.1% to about 2.0% by weight of the alloy. In such circumstances, the addition of Sn in combination with Zn improves properties of the alloy in comparison with the addition of Sn only.

The copper alloys of the present invention demonstrate improved properties over conventional copper alloys. To facilitate a better understanding of the present invention, the following examples of preferred embodiments are given. In no way should the following examples be read to limit or define the scope of the invention.

EXAMPLES Example 1

A phosphorous deoxidized copper alloy comprises 0.1˜2.0 weight-weight percentage (w/w %) of the element Sn, which forms an alpha solid solution in the phosphorous deoxidized copper as the matrix.

In view of the volume of the casting furnace, 0.1˜2.0% of the metal Sn as a solute was added into phosphorous deoxidized copper as a matrix solvent, forming a solid solution of the solute element in the matrix and thus a copper alloy. Accordingly the increase of the deformation resistance between crystal grains resulted in the effect of solid solution strengthening.

In order to further improve mechanical properties of the copper alloy, phosphorous deoxidized copper may be selected as the starting material to further control the contents of other elements: less than 0.004% of sulfur (S), less than 0.004% of oxygen (O), 0.01˜0.05% of phosphorus (P), as well as copper (Cu) and other impurities account for the remaining amount. Furthermore, such impurity elements as iron (Fe), nickel (Ni), chromium (Cr), silver (Ag), lead (Pb), aluminum (Al) and bismuth (Bi) should be so controlled that the total content of the impurity elements is no greater than 0.06% by weight.

It should be noted herein that the elements Zn and/or Sn form a solid solution with copper in the copper alloy, and neither Zn nor Sn is present in the form of its elementary substance. However, the content of Sn or Zn can be determined by using proper assays.

As tested, each of air-conditioner tubings made from the copper alloy of the present invention has the tensile strength of greater than 260 MPa, specific elongation of greater than 40%, and a mean crystal grain size of about 0.015 to about 0.035 mm, while the tubings made from phosphorous deoxidized copper has the tensile strength of about 230 to about 240 MPa. As confirmed with a number of assays, the tubings made from the copper alloy of the present invention have significantly improved pressure resistance, in comparison with the tubings of identical specifications from phosphorous deoxidized copper. Furthermore, in comparison with the tubings constructed from phosphorous deoxidized copper, the wall thickness of tubings made from the copper alloy of the present invention can be reduced by at least 15%, which meets normal operation pressure requirements, and significantly saves the cost of material.

A formulation of a copper alloy having 0.1˜2.0% of Sn, less than 0.004% of S, less than 0.004% of O, 0.01˜0.05% of P, as well as Cu and impurities (for the remaining), was used to produce copper alloy tubes, wherein such impurity elements as Fe, Ni, Cr, Ag, Pb, Al and Bi were so controlled that the total content of the impurity elements is less than 0.06% by weight. The samples of copper alloy tubings in soft state (upon annealing) were tested at ambient temperature (about 20° C.) in terms of tensile strength, which is listed in Table 1 below.

TABLE 1 Sn (w/w %) Tensile strength (MPa) 0.1% 260 0.45%  270 2.0% 290

As shown in Table 1, all of the samples of copper alloy tubings in soft state (upon annealing) tested at ambient temperature (about 20° C.) have a tensile strength of greater than 260 MPa, while the tubings of phosphorous deoxidized copper have a tensile strength of 205˜255 MPa. Accordingly, as the copper alloy tubings have improved tensile strength, they have correspondingly improved pressure resistance.

Parameters of the tubings made from the present copper alloy comprising Sn 0.1˜2.0% and phosphorous deoxidized copper respectively, which have a diameter of 7 mm and wall thickness of 0.24 mm are listed in Table 2 below.

TABLE 2 Phosphorous deoxidized Copper alloy copper Burst Burst Wall Burst Tensile pressure/ Burst Tensile pressure/ Diameter thickness pressure strength tensile pressure strength tensile (mm) (mm) (MPa) (MPa) strength (MPa) (MPa) strength 7.03 0.24 17.4 270 0.0644 14.2 235 0.0604 7.01 0.24 17.2 270 0.0637 14.3 238 0.0601 7.03 0.24 17.3 276 0.0628 14.4 240 0.0598 7.02 0.24 17.4 272 0.0639 14.3 240 0.0596 7.02 0.24 17.6 273 0.0643 14.2 236 0.0602 7.03 0.24 17.7 275 0.0643 14.5 237 0.0611 7.01 0.24 18.1 281 0.0645 14.5 237 0.0612 7.01 0.24 17.2 269 0.0641 14.5 238 0.0611 7.03 0.24 17.2 268 0.0642 14.3 235 0.0610 7.03 0.24 17.3 272 0.0635 14.1 235 0.0598 7.02 0.24 17.2 270 0.0638 14.1 236 0.0599 7.02 0.24 17.7 279 0.0636 14.2 236 0.0602 7.01 0.24 17.5 276 0.0635 13.9 232 0.0601 7.01 0.24 17.0 265 0.0641 14.1 230 0.0611 7.03 0.24 17.2 269 0.0641 14.1 231 0.0612

As used herein, the term “burst pressure/tensile strength” refers to the destruction force tolerable by the tubing when the tensile strengths of the tubings are the same. A high burst pressure indicates an enhanced pressure resistance. As seen clearly in Table 2, the copper tubings made from the present copper alloy have improved mechanical properties in comparison with those made from phosphorous deoxidized copper.

With respect to tensile strength, the copper alloy tubings of the present invention are significantly superior to those of phosphorous deoxidized copper in the same specification. With respect to burst pressure, the copper alloy tubings of the present invention are significantly superior to those of phosphorous deoxidized copper in the same specification. With respect to burst pressure/tensile strength, the copper alloy tubings of the present invention can tolerate a significantly higher destruction force than the tubings of phosphorous deoxidized copper in the same specification, if their tensile strengths are the same. Therefore, the copper alloy tubings exhibit better pressure resistance than the latter in the same specification.

Example 2

A phosphorous deoxidized copper alloy comprises 0.1˜2.0w/w % of the element Sn, 0.05˜1.0% of the element Zn, wherein the elements Sn and Zn form alpha solid solution in the phosphorous deoxidized copper as the matrix.

In order to further improve mechanical properties of the copper alloy, the contents of other elements may be controlled: less than 0.004% of S, less than 0.004% of O, 0.01˜0.05% of P, as well as Cu and other impurities account for the remaining amount. Furthermore, such impurity elements as Fe, Ni, Cr, Ag, Pb, Al and Bi are controlled that the total content of the impurity elements is no greater than 0.06% by weight.

A formulation of a copper alloy having 0.1˜2.0% of Sn, 0.05˜1.0% of Zn, less than 0.004% of S, less than 0.004% of O, 0.01˜0.05% of P, as well as Cu and impurities (for the remaining), was used to produce copper alloy tubes having a diameter of 7 mm, wherein such impurity elements as Fe, Ni, Cr, Ag, Pb, Al and Bi were controlled such that the total content of the impurity elements was less than 0.06% by weight. The samples of copper alloy tubings in soft state (upon annealing) were tested at ambient temperature (about 20° C.) in terms of tensile strength, which is listed in Table 3 below.

TABLE 3 Sn (w/w) Zn (w/w) Tensile strength (MPa) 0.1% 1.0% 265 0.45%  0.4% 275 2.0% 0.05%  295

As shown in Table 3, all of the samples of copper alloy tubings in soft state (upon annealing) tested at ambient temperature (about 20° C.) have a tensile strength of greater than 265 MPa, while the tubings of phosphorous deoxidized copper have a tensile strength of 205˜255 MPa. Accordingly, as the copper alloy tubings have improved tensile strength, they have correspondingly improved pressure resistance.

The invention may be better understood by reading the following description of non-limitative, exemplary embodiments with reference to the attached drawings wherein like parts of each of the figures are identified by the same reference characters.

With reference to FIG. 1, the present invention provides a method for producing a copper alloy. In step 101, at least one trace element comprising tin is preheated to substantially remove any moisture in the trace element. Step 101 is followed by step 102, in which the trace element is added to a molten solution of phosphorous deoxidized copper. After step 102, in step 103, the solution comprising the trace element is homogenized, casted, and cooled to produce a copper alloy comprising an alpha solid solution.

In certain exemplary embodiments, the content of tin ranges from about 0.1% to about 2.0% by weight of the copper alloy. If the content of Sn is less than 0.1% by weight of the alloy, the solid solution strengthening effect exhibits no significant advantage in comparison with conventional alloys. Furthermore, in the instance that the content of Sn is greater than 2.0% by weight of the alloy, the tensile strength of the resulting alloy material is improved, however, the properties of the alloy material severely impede the machining of the material, and accordingly, would hinder tubing production.

In certain embodiments, the element zinc (Zn) may be added to a molten fluid of copper, which further improves the solid solution strengthening, and has improved mechanical properties. Moreover, the addition of Zn may reduce the size of crystal grains, which may improve mechanical properties of the alloy material. In certain exemplary embodiments, the content of Zn ranges from about 0.05% to about 1.0% by weight of alloy. In certain exemplary embodiments, the content of Zn added may be about 1.0% by weight of the alloy, where the content of Sn is 0.1% by weight of the alloy. In an alternative embodiment, the content of Zn added may be 0.05% by weight of the alloy, where the content of Sn is 2.0% by weight of the alloy. That is, the content of Zn added may range from about 0.05% to about 1.0% by weight of the alloy, where the content of Sn ranges from about 0.1% to about 2.0% by weight of the alloy. In such circumstances, the addition of Sn in combination with Zn improves properties of the alloy in comparison with the addition of Sn only.

In order to further improve mechanical properties of the copper alloy, phosphorous deoxidized copper may be selected as the starting material to further control the contents of other elements: less than 0.004% of sulfur (S), less than 0.004% of oxygen (O), 0.01-0.05% of phosphorus (P), as well as copper (Cu) and other impurities account for the remaining amount. Furthermore, such impurity elements as iron (Fe), nickel (Ni), chromium (Cr), silver (Ag), lead (Pb), aluminum (Al) and bismuth (Bi) should be so controlled that the total content of the impurity elements is no greater than 0.06% by weight. In certain exemplary embodiments, the copper alloy of the present invention includes 0.45% by weight of Sn, less than 0.004% of S, less than 0.004% of O, 0.01˜0.05% of P, and the total content of the impurity elements is less than 0.06% by weight.

With reference to FIG. 2, the present invention provides another method for producing a copper alloy. In step 201, the trace element of tin is pre-heated to substantially remove any moisture. In step 202, the amount by weight of the elements tin or both tin and zinc is determined, as well as the weight of phosphorous deoxidized copper. For example, if the casting oven has a volume of V, then the copper alloy to be produced is accordingly determined to have a weight of M. If tin is only added to the alloy to be produced, in which the content of tin is 0.45% by weight, then M×0.45% of tin is added into the casting oven, while the weight of phosphorous deoxidized copper is M−M×0.45%.

Step 202 is followed by step 203, in which tin or both tin and zinc is/are added in the predetermined amount in a single batch into the casting oven having molten phosphorous deoxidized copper in the predetermined amount. Since the trace elements to be added (Sn or Zn) have a low density and a low melting temperature, adding the tin or both tin and zinc in a single batch allows the elements to readily melt, depending on the shape and size of Sn and optionally Zn. In step 204, the trace elements of tin and optional zinc in the molten copper liquid are agitated and homogenized. Thereafter, in step 205, the copper alloy is casted into hollow or solid billet by means of horizontal continuous casting. Finally, in step 206, the hollow or solid billet is cooled to ambient temperature.

In the process of copper casting, the copper alloy is formed by adding the solute metal of Sn to phosphorous deoxidized copper as the matrix solvent, and the effect of solid solution strengthening is achieved due to the increased resistance to deformation between crystal grains. The tubes of copper alloy are constructed from the copper alloy, which is a finished product in soft state by the treatment of casting, rolling, elongating and annealing. As tested, the resulting tubes have a tensile strength of greater than about 260 MPa, specific elongation of greater than 40%, and mean crystal grain size of about 0.015 to about 0.035 mm. Moreover, under similar conditions, the tubings of the present invention have a significant higher burst pressure than that of conventional tubings from phosphorous deoxidized copper.

In certain embodiments, the present invention provides a copper alloy tube, wherein the copper alloy comprises alpha solid solution formed by phosphorous deoxidized copper and at least one trace element comprising tin. In certain exemplary embodiments, the content of tin is about 0.1% to about 2.0% by weight of the copper alloy. In certain exemplary embodiments, the trace element further comprises zinc, the content of which is about 0.05% to about 1.0% by weight of the copper alloy. The principles, methods and particular experimental data have been described in the above examples, and thereby are not described again for conciseness.

In the process of phosphorous deoxidized copper casting, the copper microalloy is formed by adding the solute metal of Sn and optionally Zn, in proper amounts in view of the volume of casting oven, to phosphorous deoxidized copper as the matrix solvent, and then forming a solid solution of the solute element in the matrix. The effect of solid solution strengthening is achieved due to increased resistance to deformation between crystal grains, thereby the copper alloy tubes of the present invention have significantly improved pressure resistance.

A copper alloy, a method for producing the copper alloy, and a copper tube derived therefrom are described above in detail. Therefore, the present invention is well adapted to attain the ends and advantages mentioned as well as those that are inherent therein. The particular embodiments disclosed above are illustrative only, as the present invention may be modified and practiced in different but equivalent manners apparent to those having ordinary skill in the art having the benefit of the teachings herein. While numerous changes may be made by those having ordinary skill in the art, such changes are encompassed within the spirit of this invention as defined by the appended claims. It is therefore evident that the particular illustrative embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the present invention. 

1. A copper alloy comprising: an alpha solid solution formed from phosphorus deoxidized copper and at least one trace element comprising tin.
 2. The copper alloy of claim 1, wherein the content of tin is from about 0.1 percent to about 2.0 percent by weight of the copper alloy.
 3. The copper alloy of claim 2, wherein the at least one trace element further comprises zinc, wherein the content of zinc is from about 0.05 percent to about 1.0 percent by weight of the copper alloy.
 4. A method for producing a copper alloy, comprising: pre-heating at least one trace element comprising tin to substantially remove moisture present in the trace element; adding the trace element to a molten solution of phosphorous deoxidized copper; and homogenizing, casting, and cooling the molten solution comprising the trace element to produce a copper alloy comprising an alpha solid solution.
 5. The method of claim 4, wherein the step of adding the trace element to the molten solution of phosphorous deoxidized copper comprises adding tin to the molten solution of phosphorous deoxidized copper, wherein the content of tin is from about 0.1 percent to about 2.0 percent by weight of the alloy to be produced.
 6. The method of claim 5, wherein the at least one trace element further comprises zinc, and wherein the step of adding the trace elements to the molten solution of phosphorous deoxidized copper further comprises adding zinc to the molten solution of phosphorous deoxidized copper, wherein the content of zinc is from about 0.05 percent to about 1.0 percent by weight of the alloy to be produced.
 7. A copper tube comprising: a copper alloy comprising an alpha solid solution formed from phosphorus deoxidized copper and at least one trace element comprising tin.
 8. The copper tube of claim 7, wherein the content of tin is from about 0.1 percent to about 2.0 percent by weight of the copper alloy.
 9. The copper tube of claim 8, wherein the at least one trace element further comprises zinc, wherein the content of zinc is from about 0.05 percent to about 1.0 percent by weight of the copper alloy. 